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Rover 420 high tickover

My '97 400 GSi (2.0 petrol T-series) occasionally ticks over too high, around 1500rpm or so. This only seems to happen after driving on the motorway - ie. after higher speeds / rpm - and won't normally happen on my commute to work which is A-roads and not more than 60mph. It ticks over normally when started from cold, just over 1000rpm compared to normal idle speed of 850rpm when warm.

Does anyone know what might cause this? At a guess I'm thinking it might be a temperature sensor not reading right at one far end of the scale making the ECU think the engine is cold when actually it's at its hottest...?

Could take it to the Rover dealer at £55+VAT per hour, but if it's a common fault I'd rather try replacing things and see what happens!

Reply to
Andrew
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Try the water temp sensor, this tells the ECU to richen the mixture when cold. Yours could be breaking down after under stress afer a long run.

Also suspect the throttle stepper motor unit, either gummed up or faulty. This can have the same effect you have described.

Rdgs

PDH

Reply to
Paul Hubbard

Andrew, don't know if this will help, or is relevant, but a friend of mine used to get engine stopping symptoms occasionally after motorway runs (214

1994). Although he never got to the bottom of it andlearned to live with it I had an inkling it may have been what you suggested, a sensor (probably water temp or air inlet temp), but he could never reproduce it when I was in the car. He always said it occurred on the slip road or roundabout so I concluded that the heat soak from the engine had caused this type of "out of limits" reading (higher than usual temperature) and put the choke on.

I suppose if you suspect this type if fault you can stop the engine, remove a spark plug, and check for signs of a rich mixture. Alterenatively there are several PC interfaces available which can read some of the ECU data, and these are very useful for eliminating possible causes. I found Gendan very helpful before buying a £70 unit which saved me changing the MAF sensor erroneously and paid for itself twice over in one diagnostic (compared to my local main dealer who said they would "start with the MAF sensor, then look again if that didn't cure it!). Google it (Gendan.co.uk?) My problem with my diesel 75 is not related to yours, by the way, just used it as an example.

Hope this helps.....PJ

Reply to
Philip Jackson

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